Low power protocol for wireless terminal peer-to-peer communications

ABSTRACT

A Wireless Local Area Network (WLAN) system in which wireless terminals each operate upon battery power. One of the wireless terminals acts as a Master to coordinate the transmission and receptions of the Slaves so as to reduce the power consumed by all of the devices. The Slaves operate according to a power up and power down sequence to conserve battery power. Further, the terminals may alternate between being Slaves and being the Master to equalize battery consumption of the wireless terminals.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional ApplicationSer. No. 60/466,377, filed Apr. 29, 2003, which is incorporated hereinby reference in its entirety for all purposes.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to wireless local area networks;and more particularly to a protocol for peer-to-peer communications ofwireless terminals.

[0004] 2. Background of the Invention

[0005] Communication technologies that link electronic devices in anetworked fashion are well known. Examples of communication networksinclude wired packet data networks, wireless packet data networks, wiredtelephone networks, wireless telephone networks, and satellitecommunication networks, among other networks. These communicationnetworks typically include a network infrastructure that services aplurality of client devices. Wired Local Area Networks (LANs), e.g.,Ethernets, are quite common and support communications between networkedcomputers and other devices within a serviced area. LANs also often linkserviced devices to Wide Area Networks (WANs) and the Internet. Each ofthese networks is generally considered a “wired” network, and thedevices on those networks have essentially unlimited power suppliessince they are connected to a wired power source.

[0006] Wireless networks have been in existence for a relatively shorterperiod. Cellular telephone networks, wireless LANs (WLANs), andsatellite communication networks, among others, are examples of wirelessnetworks. Relatively common forms of WLANs are IEEE 802.11 (a) networks,IEEE 802.11 (b) networks, and IEEE 802.11 (g) networks, referred tojointly as “IEEE 802.11 networks.” IEEE 802.11 networks may operateeither in Infrastructure Mode or in Ad Hoc mode. In Infrastructure Mode,a single node, termed an Access Point (AP), coordinates the actions ofthe other nodes and typically provides a connection to a wired network.In Ad Hoc mode, where an AP is not present, the wireless nodes jointlycoordinate the WLAN. In IEEE 802.11 networks, the nodes may coordinatein one of two possible methods: the Distributed Control Function (DCF)or the Point Control Function (PCF). It is generally assumed that aPoint Coordinator (PC) that provides the PCF is an AP within an IEEE802.11 network operating in Infrastructure Mode.

[0007] WLANs provide significant advantages when servicing portabledevices such as portable computers, portable data terminals, portablegame terminals and other devices that are neither typically stationarynor tethered to power. Because these devices are battery powered, it isadvantageous for these devices to turn off their radios and processingblocks as often as possible to conserve power. When an AP services theWLAN, the AP is usually tethered to a LAN connection and is connected toa wired power source. The AP therefore can continuously provide the PCFwithout interruption. However, in an Ad Hoc network, each of the WLANdevices is a peer such that none of the devices serves as an AP. Ad Hocnetworks may require transmission coordination similar to that providedby the IEEE 802.11 PCF since all of the devices are peers. In atraditional system, the transmitter and receiver of the PC typicallyremain constantly powered via a wired source. In an Ad Hoc network, alldevices may be battery powered so that none of the devices mayreasonably service the PCF.

[0008] In the current IEEE 802.11 specification when operating in thePCF mode, devices (CF-pollable STA) may only transmit data when theyhave received a poll from the PC. After the device has transmitted itsdata, it expects to receive an acknowledgement message. If the dataframe is not in turn acknowledged, the CF-Pollable STA shall notretransmit the frame unless the PC polls it again, or it decides toretransmit during the Contention Period (CP). (Section 9.3 of IEEE802.11 specification.) Thus the specified PC may receive transmissionswhen it is not powered and/or the PC may unnecessarily remain poweredawaiting potential retransmissions.

[0009] Thus, there is a need in the art for improvements in protocolsfor WLAN peer devices that not only coordinate transmissions of peersthat results in reduced power consumption, but that supports robust datathroughput.

SUMMARY OF THE INVENTION

[0010] In order to overcome the shortcomings of the prior systems andmethods of operation, a method according to the present inventionmanages peer-to-peer communications in a wireless Local Area Network(WLAN) among a plurality of wireless terminals using a unique framecycle.

[0011] The frame cycle includes a beaconing period, a broadcast dataperiod, a plurality of polled data periods, and a contention period. Oneof the plurality of wireless terminals acts as a Master during eachframe cycle and the remaining ones of the plurality of wirelessterminals act as Slaves during each frame cycle. During the beaconingperiod, the Master transmits a beacon and each of the plurality ofSlaves listens for the beacon. During the broadcast data period, theMaster broadcasts data and each of the plurality of Slaves listens forthe broadcast data. During each polled data period, the Master polls anassigned Slave and the assigned Slave transmits data to the Master if ithas data to send. During the contention period, new Slaves that arepresent within the WLAN transmit to the Master in an attempt to become amember of the WLAN.

[0012] The frame cycle allows the wireless terminals to conserve batterylife by powering down their transmitters and receivers during selectperiods of time. During the plurality of polled data periods,non-assigned Slaves power down their transmitters and receivers. Duringthe contention period, the plurality of Slaves power down theirtransmitters and receivers also. Such is the case because during theseperiods the Slaves that are already members of the WLAN do not interfacewith the Master.

[0013] The method further includes optionally alternating masteringduties among the plurality of wireless terminals according to around-robin mastering cycle. Because the round-robin mastering cycledoes not require a single wireless terminal to be Master at all times,battery drain is distributed amongst all the wireless terminals of theWLAN. In one embodiment of the round-robin mastering cycle, none of thewireless terminals serves as the Master for consecutive frame cycles. Inanother embodiment of the round-robin mastering cycle, none of thewireless terminals serves as the Master for more than one frame cycle ofthe plurality of frame cycles. In still another embodiment of theround-robin mastering cycle, one of the wireless terminals acts as theMaster for more than one consecutive frame cycle of the plurality offrame cycles.

[0014] During the beaconing period and the broadcast data period, atleast one Slave of the plurality of Slaves powers down its respectivetransmitter because during the beaconing period and the broadcast dataperiod the Slaves are not required to transmit to the Master. Eachpolled data period corresponds to a particular Slave of the plurality ofSlaves. Polled data period assignments are broadcast to the plurality ofSlaves during the beaconing period. Because each Slave knows itsassigned polled data period, each Slave may power down its transmitterand receiver during non-assigned polled data periods. During assignedpolled data periods, the Slaves power up their transmitters andreceivers so that they can transmit data to the Master and receiveacknowledgements from the Master.

[0015] The polled data period may be subdivided into a polling period, adata transmission period, and an acknowledgement period. With thissubdivision, an assigned Slave ramps up power to its receiver prior tothe polling period, ramps up power to its transmitter prior to the datatransmission period, fully powers its transmitter and receiver duringthe data transmission period during which it transmits data to theMaster, and powers down its transmitter during the acknowledgementperiod. During the acknowledgement period, the Slave keeps its receiverpowered so that it can receive an acknowledgement from the Master. Ifsuch an acknowledgement is not received, the Slave will again transmitthe data to the Master during the next frame cycle.

[0016] Moreover, other aspects of the present invention will becomeapparent with further reference to the drawings and specification, whichfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] These and other features, aspects and advantages of the presentinvention will be more fully understood when considered with respect tothe following detailed description, appended claims and accompanyingdrawings wherein:

[0018]FIGS. 1A and 1B are system diagrams illustrating a plurality ofwireless terminals and their operation generally according to anembodiment of the present invention;

[0019]FIG. 2 is a block diagram illustrating a wireless terminalconstructed according to the present invention;

[0020]FIG. 3 is a flow diagram illustrating operation according to oneembodiment of the present invention;

[0021]FIG. 4 is a block diagram illustrating the frame cycle division ofan embodiment of the present invention; and

[0022]FIG. 5 is a signal timing diagram illustrating one example ofoperation according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0023]FIGS. 1A and 1B are system diagrams illustrating a plurality ofwireless terminals and their operation generally according to anembodiment of the present invention. As shown in FIG. 1A, a wirelesslocal area network (WLAN) includes a plurality of wireless terminals306, 308, 320, 322, and 324. These wireless terminals operate accordingto the present invention such that during any frame cycle, one of thewireless terminals, e.g., wireless terminal 324, serves as the Masterand remaining ones of the wireless terminals act as Slaves. Thisdesignation of Masters and Slaves remains in force for the particularframe cycle. When round-robin mastering is being used, the designationof the Master may change every frame cycle or may change every so often.With the round-robin mastering cycle of the present invention, each ofthe Slaves will typically serve as a Master for at least one frame cycleof the plurality of frame cycles of the round-robin mastering cycle.

[0024] If it is determined that one of the wireless terminals istethered to a power source, e.g., laptop computer 306 or 308, thetethered wireless terminal may be the assigned Master while the deviceis tethered. This operation will reduce battery drain of the otherwireless devices. Mastering assignment may be performed in an effort todistribute Mastering duties among the plurality of wireless terminals touniformly drain the batteries of the wireless devices. In such case,wireless devices having comparatively longer battery lives will havegreater Mastering duties.

[0025]FIG. 1B is a system diagram illustrating the wireless devices 306,308, 320, 322, and 324. Comparing FIG. 1B from FIG. 1A, a new Master,wireless terminal 322, has been assigned for the particular frame cycleillustrated in FIG. 1B. In such case, wireless devices 306, 308, 320,and 324 operate as Slaves to the Master for the particular frame cycle.This designation of Masters and Slaves may continue for one or aplurality of frame cycles of the round-robin mastering cycle. The mannerin which the wireless terminals of FIGS. 1A and 1B operate are describedin more detail with reference to FIG. 2 through FIG. 5.

[0026]FIG. 2 is a block diagram illustrating a wireless terminalconstructed according to the present invention. A wireless terminal 200includes an RF unit 204, a processor 206, a memory 208, and a userinterface 210. The RF unit 204 couples to an antenna 222 that may belocated internal or external to the case of the wireless terminal 200.In another embodiment, the wireless terminal 200 may include multipleantennas. The RF unit 204 includes a transmitter 216 and a receiver 218that couple to the antenna 222 via a transmit/receive switch 220.

[0027] The processor 266 may be an Application Specific IntegratedCircuit (ASIC) or another type of processor that is capable of operatingthe wireless terminal 200 according to the present invention. The memory208 includes both static and dynamic components, e.g., DRAM, SRAM, ROM,EEPROM, etc. In some embodiments, the memory 208 may be partially orfully contained upon an ASIC that also includes the processor 206. Auser interface 210 includes a display, a keyboard, a speaker/microphone,and/or a data interface, and may include other user interfacecomponents. The RF unit 204, the processor 206, the memory 208, and theuser interface 210 couple via one or more communication buses/links. Abattery 212 also couples to and powers the RF unit 204, the processor206, the memory 208, and the user interface 210. The structure of thewireless terminal 200 illustrated is only an example of one wirelessterminal structure. Many other varied wireless terminal structures couldbe operated according to the teachings of the present invention.

[0028] In performing the operations of the present invention, thewireless terminal 200 may execute software instructions, i.e., WLANInstructions (WIs) 214. WIs 214 enable the wireless terminal 200 toperform the operations of the present invention. In executing thewireless instructions, the WIs 214 are loaded from memory 208 into theprocessor 206 for execution. In other embodiments, however, the wirelessterminal 200 may operate according to the present invention based uponhardware function, firmware instructions, or a combination of any/all ofthese.

[0029]FIG. 3 is a flow diagram illustrating operation according to oneembodiment of the present invention. As is illustrated in FIG. 3, duringeach frame cycle of the round-robin mastering cycle a Master is firstassigned or reassigned (step 302). The determination of which wirelessterminal of the WLAN to assign as the Master may be a very structuredmethodology in which each wireless terminal will serve as the Master forone or a plurality of frame cycles of the round-robin mastering cycle.Another technique may include a determination of which wirelessterminals are best suited to be Masters and to use these wirelessterminals as Masters while having other of the wireless terminals notserve as Masters during the round-robin mastering cycle. In any case,for the particular frame cycle of the round-robin mastering cycle, aMaster will be assigned or reassigned.

[0030] For the particular frame cycle, remaining wireless terminals actas Slaves (step 304). With this Master and Slave designation processcompleted, operation enters the beaconing period in which the Mastertransmits a beacon and the Slaves listen to the beacon (step 306).During the beaconing period the Slaves may power down their transmittersto conserve battery life. With the beaconing period completed, operationof the frame cycle continues into the broadcast data period (step 308).In the broadcast data period, the Master transmits data and the Slaveslisten for data and receive the data. During the broadcast data period,the Slaves may power down their transmitters because the transmittersare not required to respond to the data transmitted by the Master.

[0031] With the beaconing period and the broadcast data periodcompleted, operation proceeds to the polled data period or periods (step310). In one embodiment of operation, each frame cycle will include apolled data period for each Slave. During each polled data period, theMaster sends a poll to each of the Slaves, and each Slave transmits datato the Master in response to the poll. The Master receives the data and,if the data is intended for another of the wireless terminals, transmitsthe data to an intended Slave during a subsequent frame cycle. Suchtransmission will occur when the device is again serving in the Mastercapacity and during the broadcast data period.

[0032] During the polled data period, non-assigned Slaves power downtheir transmitters and receivers (step 312). The non-assigned Slaves maydo this because they wish to conserve power during the non-assignedpolled data period. During the assigned polled data period, the assignedSlave powers its transmitter and receiver (step 314). Then, for theexchange between the Master and the Slave, the Master polls the assignedSlave, receives data from the assigned Slave, and sends anacknowledgement to the assigned Slave (step 316). Concurrently, theassigned Slave receives the poll from the Master, transmits data to theMaster, and receives an acknowledgement from the Master (step 318).

[0033] Continuing with the operation of the frame cycle, the Masterdetermines whether or not the last polled data period has been completed(step 320). If not, operation proceeds to the next assigned Slave in thepolled data period (step 312). If the polled data period is complete,operation proceeds to the contention period in which, for example, theMaster listens for new Slaves (step 322). The member Slaves may powerdown their transmitters and receivers during the contention periodbecause they generally do not transmit to the Master nor receive fromthe Master. In one embodiment, member slaves may need to retransmit dataduring the contention phase. Non-member wireless terminals desiringentry into the WLAN transmit to the Master during the contention period,requesting admittance to the WLAN (step 324). In the contention period,the Master may power down its transmitter and leave its receiver poweredduring what is referred to as a new Slave waiting period. This is theperiod during which it is expected that any Slave requesting admittanceto the WLAN will respond to the Master. From step 324 operation proceedsto step 302, where a new Master may be assigned or reassigned.

[0034] In most wireless devices, it takes some time to ramp up the powerto a receiver or transmitter before communications may be serviced.According to some embodiments of the present invention, the receiverand/or transmitter is/are left powered during periods that do notrequire corresponding transmit or receive functionality. The device(s)are left powered during this/these period(s) so that the device(s) willfunction during a following interval when required.

[0035]FIG. 4 is a block diagram illustrating the frame cycle division ofan embodiment of the present invention. The structure of FIG. 4illustrates the various operations of the Masters and Slaves during theframe cycle division of the frame cycle. During the beaconing period402, the Master powers up both its transmitter and receiver. However, inother operations, the Master may not power its receiver because it isonly transmitting during the beaconing period 402 and not listening.During the beaconing period 402, the Slaves must power their receivers,but their transmitters may not powered in order to conserve batterylife. During the broadcast data period 404, the Master has itstransmitter and receiver powered. The Slaves, however, only receivingdata from the Master, will have their receivers powered but not theirtransmitters powered.

[0036] The polled data periods will include a first polled data period406A, a second polled data period, and so on through the “Nth” polleddata period 406N. During each polled data period, there will be anassigned Slave and a plurality of unassigned Slaves. During each polleddata period, the Master will have both its receiver and transmitterpowered because it transmits a poll to the assigned Slave, waits fordata from the assigned Slave, and transmits an acknowledgement to theassigned Slave. Thus, the polled data period may be subdivided into apolling period, a data transmission, and an acknowledgement period.During each polled data period, unassigned Slaves are neither receivingnor transmitting.

[0037] During the first polled data period 406A, a first assigned Slavemay transmit data to the Master. Because the Slave has data to transmitand because it must also listen for the poll and for an acknowledgement,the Slave must have both its transmitter and receiver powered during atleast some portions of the assigned poll data. Because the firstassigned Slave had its receiver powered during the broadcast data period404, the first assigned Slave leaves its receiver powered from thebroadcast data period 404 through the first polled data period 406A.However, the first assigned Slave must power its transmitter for receiptof the pole from the Master. Thus, the first assigned Slave may ramp upits transmitter during the polling period at a sufficient rate to beready just before the end of the incoming pole from the Master. Duringthe data transmission period of the first poled data period 406A, thefirst assigned Slave transmits data to the Master. After thistransmission is complete, the first assigned Slave may power down itstransmitter. However, the first assigned Slave must keep its receiverpowered up after the data transmission period so that it will receivethe acknowledgement during the acknowledgement period. After theacknowledgement period, the first assigned Slave may power down itsreceiver.

[0038] During the other polled data periods, the assigned Slaves operatein a similar fashion. Because the other assigned Slaves have had theirreceivers and transmitters powered down during prior unassignedpolled-data periods, they must ramp up power to their transmitters andreceivers for their assigned polled-data periods. During the datatransmission period, the transmitter and the receiver of the assignedSlave are both powered. However, after the data transmission period, theassigned Slave may ramp down or turn off power to its transmitter whilekeeping its receiver powered for the acknowledgement period. After theassigned polled data period has been completed, the assigned Slave maypower down both its transmitter and its receiver.

[0039] The contention period 408 is the portion of the frame of theframe cycle in which new Slaves may request entry to the WLAN. In suchcase, the Master has only to listen for new Slaves and thus does notpower its transmitter. The Master does power its receiver for aSlave-waiting period, during which new Slaves may request admittance tothe WLAN. After the Slave-waiting period, the Master may power down itsreceiver, as well as its transmitter. During the contention period, allSlaves that are members of the WLAN will power down both theirtransmitters and their receivers.

[0040]FIG. 5 is a signal timing diagram illustrating one example ofoperation according to an embodiment of the present invention. Thedesignations of Slave(A), Slave(B), and Slave(C) may correspond to thedesignations of FIG. 1A or 1B, for example. Row 800 shows the Mastertransmit signals, row 820 shows the Slave(A) transmit signals, row 825shows the Slave(B) transmit signals, and row 830 shows the Slave(C)transmit signals. Row 840 shows the power state of the Mastertransmitter components and row 850 shows the power state of the Masterreceiver components. Row 860 shows the power state of the Slave(A)transmitter components and row 870 shows the power state of the Slave(A)receiver components. Row 880 shows the power state of the Slave(C)transmitter components and row 890 shows the power state of the Slave(C)receiver components.

[0041] The Master 324 begins the frame cycle 815 by transmitting abeacon during beaconing period 801. Slave(A), Slave(B), and Slave(C)receive the beacon from the Master 324 during the beaconing period 801.The Master 324 waits a period of time (for example a Short InterFrameSpace (SIFS) period (not shown)) and then simultaneously transmitsbroadcast data 802 to Slave(A), Slave(B), and Slave(C) during thebroadcast data period 802.

[0042] In either the Beacon transmission or the Broadcast datatransmission, the Master notifies the Slaves of the polled-data periodassignments. As illustrated in FIG. 5, the first polled-data period isassigned to Slave(A), the second polled-data period is assigned toSlave(B), and the third polled-data period is assigned to Slave(C). Thisorder may change from frame cycle to frame cycle. The Master 324 waits aperiod (for example SIFS period) and then transmits a poll request toSlave(A) during the polling period 803 of the polled-data period. TheMaster 324 waits to receive data 821 from Slave(A) during the datatransmission period 804 of the first polled-data period and, after aperiod, Slave(A) transmits Data(A) 821 to the Master. After the Masterhas correctly received Data(A) 821, it waits a period then transmits anAcknowledgement(A) to Slave(A) and a Poll(B) to Slave(B) during thecombined acknowledgement period/polling period 805. During datatransmission period 806, the Master receives Data(B) 826 from Slave(B).After the Master has correctly received Data(B) 826, it waits a periodthen transmits Acknowledgement(B) to Slave(B) and Poll(C) to Slave(C)during combined acknowledgement period/polling period 807. The Masterreceives Data(C) 831 from Slave(C) during data transmission period 808.After Master has correctly received Data(C) 831, it waits a period thentransmits Acknowledgement(C) and CFEND during acknowledgement period809.

[0043] Operation then enters the contention period. In the contentionperiod, the Master waits to receive transmissions from new slavesrequesting to join the WLAN. If no transmissions have been receivedwithin the new Slave Waiting Period 811, the Master ceases listening. Atthe end of the contention period 810, a new frame cycle commences with anew Beacon 819. In the new frame cycle the Master may be a differentwireless terminal or may be the same wireless terminal.

[0044] Referring to both FIGS. 2 and 5, the processor 206 of eachwireless terminal executes WLAN instructions (WIs) 214 to turn offcomponents of the wireless terminal 200 to reduce the power drawn frombattery 212. Typically, various components within the receiverfunctionality or transmitter functionality in the RF unit 204 and theprocessor 206 are controlled to conserve battery life. A related aspectis that various components and functions in the RF unit 204 may takeramp or stabilization time before operating properly or optimally for aperiod of time after power is applied. Thus components must be turned onfor a period of time before needed.

[0045] An example of this type of power management is illustrated withreference to the Slave(A) transmitter power 860. Slave(A) is notrequired to transmit during the Beacon period 801 or the Broadcast dataperiod 802 and its transmit components are turned off (sleep) 861 duringthese portions of the frame cycle 815. In preparation for transmittingData(A) 821, Slave(A) begins to power on sub-components of itstransmitter during Ramp 862. During Ramp 862, different sub-componentsare turned on at different times as illustrated in 862. For example, aCrystal Oscillator and a Synthesizer of the transmitter are turned on1000 microseconds before needed and a Phase Lock Loop (PLL) of thetransmitter is turned on 100 microseconds before needed. The transmitteris then optimally available for transmission of Data(A) 821. Duringtransmission of Data(A) 821, the transmitter is fully on as indicated at863. After the transmission Data(A) 821 is completed, the transmitter isreturned to a sleep mode at 864. Such power control steps significantlyreduce the average power drawn from the battery 212 in the wirelessterminal 200. Similar operations are performed for the other componentsand functionality in the wireless terminal 200 such as in the RFreceiver 218. Similar operations are performed for each other of theSlaves and for the Master.

[0046] A particular embodiment of the present invention rotates theorder that the Slaves (Slave(A), Slave(B), and Slave(C)) are assignedpolled-data periods so as to equalize the average amount of power drawnover multiple frame cycles 815. In a rotation of the Slave order,Slave(B) becomes Slave(A), Slave(C) becomes Slave(B), Slave(D) becomesSlave (C), and Slave(A) becomes Slave(D) in a last operation of thecycle. Such a rotation can occur every cycle or every “n” cycles.Further, this cycle may be extended for additional Slave devices.

[0047] Another particular embodiment of the present inventionperiodically swaps the role of the Master 324 with a device that was aSlave so as to equalize the average amount of power drawn over multipleframe cycles 815. This rotation is an integer multiple greater than oneof the number of cycles that the Slaves rotate. The Master is swappedfor Slave(A). The integer multiple is selected so that a differentphysical device is the old Slave(A) each time that the Master is swappedfor Slave(A).

[0048] When a new Slave, for example Slave(D) wishes to enter thecommunication system, it does so by transmitting a message during thecontention period 810. A further use of the contention period 810 is ifa Slave does not receive an acknowledgement to its data message, thedata message may have become corrupted during transmission. Thus, thedata message must be retransmitted. The data message is notretransmitted during the contention free period since it would disturbthe pattern when the other Slaves are expecting to wake up so as toreceive and transmit their messages. Retransmissions are alsotransmitted during the contention period. In order to minimize potentialcollisions during the contention period, the Slaves retransmit in theorder in which they were polled. Since it is unlikely that all of theSlaves must retransmit in the same cycle, a deferring mechanism isestablished to reduce the time the Master must wait with its receiveron. Slave(A) must wait a single period of time (for example a SIFS time)before transmitting after CFEND 809. Slave(B) must wait two periods oftime (for example two SIFS times) before transmitting after CFEND 809.Slave(C) must wait three periods of time (for example three SIFS times)before transmitting after CFEND 809, and so on. Finally, a potential newSlave may transmit a new Slave message after another period of time (forexample SIFS time) duration. Thus, the maximum time a Master needs tomaintain its receiver without receiving a signal after CFEND 809 isperiod of time (for example SIFS) times the number of Slaves plus one inthe frame cycle 815.

[0049] If more than one Slave must retransmit, each Slave decrements thenumber of period of time (for example a SIFS times) it waits by one foreach retransmission that occurs. The next retransmission may then beginafter the successful transmission and acknowledgement of the previousretransmission followed by the number of SIFS periods calculated above.Before transmitting, a Slave must check to make sure no othertransmission is occurring. No retransmission may occur after the end ofthe current frame cycle 815. Before transmitting, a Slave must check tomake sure that the duration of its transmission would exceed the end ofthe current frame cycle 815. Since the Slaves defer theirretransmissions by different amounts of time, a time and power consumingcollision is unlikely.

[0050] Another embodiment of the invention used in conjunction with thestructured transmission times identifies the compression of thesubsequent headers of the transmission messages according to informationgiven during the Broadcast data 802. For example, the 6 octet MACaddress within a header may be substituted with a single octet Masterderived ID. The mapping is conveyed in the Broadcast data 802 and isused by the Slaves and Master for all message header transmissions inthat frame cycle.

[0051] The invention disclosed herein is susceptible to variousmodifications and alternative forms. Specific embodiments therefore havebeen shown by way of example in the drawings and detailed description.It should be understood, however, that the drawings and descriptionthereto are not intended to limit the invention to the particular formdisclosed, but on the contrary, the invention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the present invention as defined by the claims.

1. A method for managing peer-to-peer communications in a Wireless LocalArea Network (WLAN) having a plurality of wireless terminals, one ofwhich acts as a master at any time and remaining ones acting as slavesat any time, the method comprising: communicating according to a framecycle including a beaconing period, a broadcast data period, a pluralityof polled data periods, and a contention period; during the beaconingperiod, the master transmitting a beacon and each of the plurality ofSlaves listening for the beacon; during the broadcast data period, themaster broadcasting data and each of the plurality of Slaves listeningfor the broadcast data; during each polled data period, the masterpolling an assigned Slave and the assigned Slave transmitting data tothe master if it has data to send; during the contention period, a newSlave, if present, transmitting to the master; during the plurality ofpolled data periods, non-assigned Slaves optionally powering down theirtransmitters and receivers; and during the contention period, theplurality of Slaves optionally powering down their transmitters andreceivers.
 2. The method of claim 1, further comprising alternatingmastering duties among the plurality of wireless terminals according toa round-robin mastering cycle, the round-robin mastering cycle includinga plurality of frame cycles, one of the plurality of wireless terminalsacting as a master during each frame cycle and remaining ones of theplurality of wireless terminals acting as Slaves during each framecycle.
 3. The method of claim 2, further comprising none of the wirelessterminals serving as the master for consecutive frame cycles of theround-robin mastering cycle.
 4. The method of claim 2, furthercomprising none of the wireless terminals serving as the master for morethan one frame cycle of the plurality of frame cycles of the round-robinmastering cycle.
 5. The method of claim 2, further comprising one of thewireless terminals acting as the master for more than one consecutiveframe cycle of the plurality of frame cycles of the round-robinmastering cycle.
 6. The method of claim 1, wherein during both thebeaconing period and the broadcast data period, at least one Slave ofthe plurality of the Slaves powers down its respective transmitter. 7.The method of claim 1, further comprising: during the beaconing period,a Slave determining that it has been assigned a polled data period thatimmediately follows the broadcast data period; the Slave powering downits transmitter during the beaconing period; and the Slave powering upits transmitter during the polled data period immediately following thebroadcast data period.
 8. The method of claim 1, further comprising:during the beaconing period, a Slave determining that it has beenassigned a polled data period that does not immediately follow thebroadcast data period; the Slave powering down its transmitter duringthe beaconing period; the Slave powering down its receiver during thepolled data period immediately following the broadcast data period; andthe Slave powering up its transmitter and its receiver during itsassigned polled data period.
 9. The method of claim 1, furthercomprising, during the plurality of polled data periods, Slaves poweringdown their transmitters and receivers during unassigned polled dataperiods.
 10. The method of claim 1, wherein the polled data periodincludes a polling period, a data transmission period, and anacknowledgement period, and the method further comprising: an assignedSlave ramping up power to its transmitter during the polling period; theassigned Slave fully powering its transmitter during the datatransmission period; and the Slave powering down its transmitter duringthe acknowledgement period.
 11. The method of claim 10, furthercomprising the assigned Slave powering its receiver during the pollingperiod, the data transmission period, and the acknowledgement period.12. The method of claim 1, further comprising the plurality of Slavespowering up their receivers after the contention period in anticipationof the next beaconing period.
 13. The method of claim 1, furthercomprising the master powering down its transmitter during thecontention period.
 14. The method of claim 13, further comprising themaster powering down its receiver during the contention period after anew Slave-waiting period expires.
 15. A system for managing peer-to-peercommunications in a Wireless Local Area Network (WLAN) having aplurality of wireless terminals, the system comprising: a plurality offrame cycles, one of the plurality of wireless terminals acting as amaster during each frame cycle and remaining ones of the plurality ofwireless terminals acting as Slaves during each frame cycle; each framecycle comprising a beaconing period, a broadcast data period, aplurality of polled data periods, and a contention period; wherebyduring the beaconing period, the master transmits a beacon and each ofthe plurality of Slaves listens for the beacon; whereby during thebroadcast data period, the master broadcasts data and each of theplurality of Slaves listens for the broadcast data; whereby during eachpolled data period, the master polls an assigned Slave and the assignedSlave transmits data to the master if it has data to send; wherebyduring the contention period, a new Slave, if present, transmits to themaster; whereby during the plurality of polled data periods,non-assigned Slaves optionally power down their transmitters andreceivers; and whereby during the contention period, the plurality ofSlaves optionally power down their transmitters and receivers.
 16. Thesystem of claim 15, wherein the plurality of frame cycles are organizedin a round-robin mastering cycle in which the plurality of wirelessterminals alternate mastering duties.
 17. The system of claim 16,whereby none of the wireless terminals serving as the master forconsecutive frame cycles of the round-robin mastering cycle.
 18. Thesystem of claim 16, whereby none of the wireless terminals serves as themaster for more than one frame cycle of the plurality of frame cycles ofthe round-robin mastering cycle.
 19. The system of claim 16, whereby oneof the wireless terminals acts as the master for more than oneconsecutive frame cycle of the plurality of frame cycles of theround-robin mastering cycle.
 20. The system of claim 15, whereby duringboth the beaconing period and the broadcast data period, at least oneSlave of the plurality of the Slaves powers down its respectivetransmitter.
 21. The system of claim 15, whereby: during the beaconingperiod a Slave determines that it has been assigned a polled data periodimmediately following the broadcast data period; the Slave powers downits transmitter during the beaconing period; and the Slave powers up itstransmitter during the polled data period that immediately follows thebroadcast data period.
 22. The system of claim 15, whereby: during thebeaconing period a Slave determines that it has been assigned a polleddata period not immediately following the broadcast data period; theSlave powers down its transmitter during the beaconing period; the Slavepowers down its receiver during the polled data period immediatelyfollowing the broadcast data period; the Slave powers up its transmitterand its receiver during its assigned polled data period.
 23. The systemof claim 15, whereby, during the plurality of polled data periods,Slaves power down their transmitters and receivers during unassignedpolled data periods.
 24. The system of claim 15, wherein the polled dataperiod includes a polling period, a data transmission period, and anacknowledgement period, and whereby: an assigned Slave ramps up power toits transmitter during the polling period; the assigned Slave fullypowers its transmitter during the data transmission period; and theSlave powers down its transmitter during the acknowledgement period. 25.The system of claim 24, whereby the assigned Slave powers its receiverduring the polling period, the data transmission period, and theacknowledgement period.
 26. The system of claim 15, whereby theplurality of Slaves power up their receivers after the contention periodin anticipation of the next beaconing period.
 27. The system of claim15, whereby the master powers down its transmitter during the contentionperiod.
 28. The system of claim 27, whereby the master powers down itsreceiver during the contention period after a new Slave-waiting periodexpires.
 29. A system for managing peer-to-peer communications in aWireless Local Area Network (WLAN) having a plurality of wirelessterminals, the system comprising: means for communicating according to aframe cycle including a beaconing period, a broadcast data period, aplurality of polled data periods, and a contention period; means for,during the beaconing period, the master transmitting a beacon and eachof the plurality of Slaves listening for the beacon; means for, duringthe broadcast data period, the master broadcasting data and each of theplurality of Slaves listening for the broadcast data; means for, duringeach polled data period, the master polling an assigned Slave and theassigned Slave transmitting data to the master if it has data to send;means for, during the contention period, a new Slave, if present,transmitting to the master; means for, during the plurality of polleddata periods, non-assigned Slaves optionally powering down theirtransmitters and receivers; and means for, during the contention period,the plurality of Slaves optionally powering down their transmitters andreceivers.